Choosing the correct furnace filter and changing it when it gets dirty is as important to your HVAC system as changing the oil is to your car. Each plays a critical function in keeping its system running safely, efficiently and for a long time.

A clogged furnace filter loses its effectiveness, allowing potentially harmful particles to move through your home. It also restricts airflow, which can damage your furnace and reduce its life span.

Ensuring your furnace uses a clean filter that is appropriate for your needs is not only about keeping your furnace operating efficiently. It’s also about delivering healthy indoor air quality for your household.

The quality of the air your family breathes is important to the heating and cooling pros at Total Assurance AC & Heating. We've long been dedicated to bettering indoor air quality in Corpus Christi. Here, we’ve answered frequent questions about HVAC filters, including that very tricky question of what direction do you point a filter in your furnace or air conditioner?

When to Replace the Air Filter in Your Furnace

It is critical to replace dirty air filters in a furnace or air conditioner periodically. Dirt-clogged filters cause the system to worker harder than it should because it takes extra work to pull air through the plugged-up filter.

Officials recommend inspecting your furnace filter every month and replacing it if it’s dirty. You’ll know if your filter needs changing because it will be gray or black from dirt or dust. Homeowners who have pets that shed will probably want to replace their furnace air filter more often, because a quality air filter will trap pet hair circulating in a home.

Where Is the Air Filter in My Furnace?

In general, a furnace air filter is usually found in the return air duct or blower compartment before the return air reaches the furnace. This ensures air entering the system is filtered before it moves through the furnace components and is heated.

Depending on the type of furnace, the filter may be positioned on the right, left, bottom or in some cases, on the inside of the furnace. It's usually housed in a slot, frame or cabinet for simple access and replacement. Always refer to your furnace's owner manual for facts concerning filter location of your furnace.

Is a Furnace Filter the Same as an Air Filter?

The straightforward answer is, yes. In HVAC, a furnace filter and an air filter or air conditioning filter are essentially the same thing. While people might refer to them differently based on the current season— hot or cold—they are all filters that clean the air in your residence.

They each get rid of dust, allergens, bacteria and other airborne debris from the air that is drawn into the furnace and air conditioning system, ensuring the air distributed throughout your home is clean and safe.

What Is the MERV Rating System and What Rating Is Best for Me?

Once you find your old furnace filter and determine when it should be changed, it’s time to choose a replacement. That means picking the level of filtration that you need. One approach to this is by picking an appropriate MERV rating for your needs.

MERV is an abbreviation for Minimum Efficiency Reporting Values. The MERV rating measures the effectiveness of air filters at trapping airborne molecules. The rating scale ranges from 1 to 20, with greater numbers indicating a greater ability to filter smaller particles.

Experts say a filter with a MERV rating between 8 and 13 offers a good balance between having good indoor air quality without needlessly restricting airflow. However, people with specific health conditions could need a a higher MERV rating.

How to Place the Air Filter in a Furnace or Air Conditioning System

Positioning an air filter in a furnace or air conditioner properly is important for the efficient operation of the heating or cooling system. Air filters are supposed to face a specific direction, indicated by an arrow printed on the side of the filter frame. The filter should be placed in the unit with this arrow pointing at the furnace or AC, which is the direction of the airflow. If you're not sure about the airflow direction, remember that air always moves from the return duct towards the heat or cooling source. Therefore, make sure the arrow points at the furnace or air conditioning unit.

Many people have difficulty remembering which direction to face their system's air filter. To help remember, consider taking a quick picture with your mobile phone after the filter has been correctly installed by a professional. Or, you also could ask a technician to use a marker to write on the outside of your furnace which direction the filter should be installed. A great time to do this is during a scheduled furnace maintenance appointment.

Changing Your Furnace's Air Filter

Changing the filter on your furnace or air conditioning system is an easy process. Here is a step-by-step breakdown of how to retreive a dirty air filter and swap it for a new one:

  1. Turn off your furnace: Make sure to shut off your furnace before starting the process.
  2. Locate the furnace filter: Typically, the filter is found within the furnace or in the air return vent. Make note of which direction the arrow points on the filter, because you’ll want the arrow on the replacement filter to point similarly.
  3. Take out the old filter: Be mindful not to knock out any dust or debris.
  4. Record the date: Write down the date of replacement on the new filter's frame. This will make it easier to keep track of when it's time for another replacement.
  5. Slide in new filter: Put in the new filter with the arrow pointing in the direction of the furnace, which is the direction of airflow and should be the same direction the arrow pointed on your last filter.
  6. Secure the filter: Make sure the new filter fits nicely and close any latches or clips that lock it in place.
  7. Turn on your furnace: Once the replacement filter is properly secured, you can turn your furnace back on.

Can a Dirty Air Filter Cause a Furnace Not to Work?

The simple answer is, yes, a dirty air filter can cause a furnace to quit working or limit its lifespan. Changing your furnace or air conditioning filter is one of the simplest things you can do to keep your system operating effectively.